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Full text of "Handbook Of Chemical Engineering - I"

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306                               CHEMICAL ENGINEERING
Hydraulic plate presses have similar general arrangements the greatest difference being that the curb is replaced by a battery of plates. Presses of this kind are used by packing houses for extracting oleo from fats in the cold. A horizontal type is used for hot stearic and oleic separations. Power plate presses are also used for expressing seeds and nuts. In pressing cotton seed, the meats after hulling the bolls and after being cooked for 20 to 30 minutes are pressed between the plates of a hydraulic press. The meats are placed in hair cloth sacks, there being one to each plate. A pressure of 3000 to 4000 Ib. per sq. in. is required and the solid material left in the sacks becomes as hard as a board under the pressing action.
Worm presses have horizontal shafts and consist of a powerful conical worm surrounded by a conical curb. The material is fed in at the large end of the worm and is advanced by it to the small end where it is discharged. During its progression the material is gradually compressed by the taper of the worm and the liquid squeezed out passes through the opening in the slats of the curb. Presses of this kind are used in the reclamation of old rubber. They can be advantageously used on some materials which have been washed to remove foreign matter or which have been digested with steam to liberate the grease and oil they contain but which still retain much liquid after a thorough draining. If the worm be mounted on a fixed hollow shaft with pierced holes the press can be used to remove oil, grease and other substance by the use of steam introduced through the hollow shaft..
Separation by Centrifugal Force.—The three possible separations which can be made by centrifugal machines are: (1) The extraction of liquids from solid material, such as textiles, fibers, leather, crystals, etc. Examples of this mode
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Extractor             Separator               Centrifuge
FIG. 28.—Laboratory convertible centrifuge.
of separation are to be seen in dyeing and extraction of excess dye and other liquids in dyeing. Extraction of molasses from raw sugar or muscovado and washing and coloring cane and beet sugar and the numerous ccntrifuging operations with massecuite in refining sugar. (2) Separation of one part of a liquid or emulsion from the balance. In adapting centrifugal machines to this end the basket of the extractor type is replaced by a curved bowl. Under rapid rotation the heavier part of the liquid will take a position next to the inner surface of the bowl and the lighter will occupy an inner ring of liquid and by a pair of pipes at the top of the'bowl, one for each of the two liquid rings formed and dipping into them continuous removal of the separated liquids may be effected. (3) In the operation called "centrifuging" the material to be separated is introduced into swivelled bottles or the swivelled receptacles affixed to a rotating shaft. On rotating, the receptacles will swing out to a straight position and the material placed in them will arrange themselves in zones, the heaviest being at the bottom of the receptacle and the lightest near the mouth. Centrifuges are much used in the laboratory for the quick estimation of volumes and weights and the test receptacles used are often graduated so that percentages of volume or weight can be read off directly. Figure 28 of a convertible laboratory machine also illustrates dia-